Department of Forest Ecology & Management, Swedish University of Agricultural Sciences (SLU), Skogsmarksgränd 17, SE-901 83 Umeå, Sweden.
Department of Forest Genetics and Plant Physiology, SLU, Skogsmarksgränd 17, SE-901 83 Umeå, Sweden.
Tree Physiol. 2022 Mar 9;42(3):513-522. doi: 10.1093/treephys/tpab127.
Boreal trees are capable of taking up organic nitrogen (N) as effectively as inorganic N. Depending on the abundance of soil N forms, plants may adjust physiological and morphological traits to optimize N uptake. However, the link between these traits and N uptake in response to soil N sources is poorly understood. We examined Pinus sylvestris L. seedlings' biomass growth and allocation, transpiration and N uptake in response to additions of organic N (the amino acid arginine) or inorganic N (ammonium nitrate). We also monitored in situ soil N fluxes in the pots following an addition of N, using a microdialysis system. Supplying organic N resulted in a stable soil N flux, whereas the inorganic N resulted in a sharp increase of nitrate flux followed by a rapid decline, demonstrating a fluctuating N supply and a risk for loss of nitrate from the growth medium. Seedlings supplied with organic N achieved a greater biomass with a higher N content, thus reaching a higher N recovery compared with those supplied inorganic N. In spite of a higher N concentration in organic N seedlings, root-to-shoot ratio and transpiration per unit leaf area were similar to those of inorganic N seedlings. We conclude that enhanced seedlings' nutrition and growth under the organic N source may be attributed to a stable supply of N, owing to a strong retention rate in the soil medium.
北方树种能够有效地吸收有机氮（N）和无机氮。根据土壤 N 形态的丰富程度，植物可能会调整生理和形态特征，以优化 N 吸收。然而，这些特征与土壤 N 源响应中的 N 吸收之间的联系还知之甚少。我们研究了欧洲赤松幼苗对有机 N（氨基酸精氨酸）或无机 N（硝酸铵）添加的生物量生长和分配、蒸腾和 N 吸收的响应。我们还使用微透析系统监测了 N 添加后盆内原位土壤 N 通量。有机 N 的供应导致土壤 N 通量稳定，而无机 N 则导致硝酸盐通量急剧增加，随后迅速下降，表明 N 供应波动，硝酸盐有从生长介质中损失的风险。与供应无机 N 的幼苗相比，供应有机 N 的幼苗的生物量更大，N 含量更高，因此 N 回收更高。尽管有机 N 幼苗中的 N 浓度较高，但根到梢的比例和单位叶面积的蒸腾与无机 N 幼苗相似。我们得出结论，由于土壤介质中保留率高，有机 N 源下增强了幼苗的营养和生长，可能归因于 N 的稳定供应。
